1. Field of the Invention
The present invention relates to a device for injecting a fixed quantity of liquid and more particularly, it relates to such device for use with automatic analysis machines for conducting bio-chemistry and blood type tests relating to bloods collected.
2. Description of the Related Art
When blood is to be transfused to a patient, biochemistry tests such as GOT and GPT, blood type tests according to ABO or Rh manner, screening to recognize irregular immune bodies in blood, tests to examine whether or not blood is infected with HBs, HBc, HIV and syphilis, and analysis of biocomponents such as .alpha.-fetoprotein and carcinoembryonic antigen which are present in an extremely fine amount in blood are conducted relating to bloods collected from other patients and blood suppliers.
In the case of the typical automatic analysis machine, these analyses are conducted in such a way that plural blood samples collected, particularly serum and blood-cells-floating liquid in the blood samples are successively injected into reaction trays by means of the liquid injection device and that reagents employed for each of the tests are injected into these reaction trays by means of the reagent injection device. The quantity of each of the blood samples to be injected must be exactly adjusted to enable the automatic analysis machine to conduct these analyses with high accuracy. Particularly in the case of analyzing .alpha.-fetoprotein and carcinoembryonic antigen in blood according to the immunological manner, or examining various kinds of infectious disease in blood, the carryover of blood must be eliminated in the course of successively injecting the blood samples into reaction trays.
In order to solve the above-mentioned problems, preliminarily-opened Japanese Patent Disclosure No. 62-247261 has proposed a liquid sucking device wherein the pipet to suck liquid sample can be disposed every time when the process of sucking the liquid sample is finished, the liquid sample is conveyed to that position where it does not reach the liquid sucking position and where its surface level is detected by a detector means, and the lowering of the pipet which is at the liquid sucking position is controlled responsive to a signal which is applied from the detector means and which represents the surface level of the liquid sample detected.
In the case of this liquid sucking device disclosed by the Japanese Patent Disclosure No. 62-247261, however, the surface level of liquid sample is detected at a position different from the liquid sucking position. This makes it necessary to drive the pipet at the liquid sucking position and also to drive the detector means at the surface level detecting position, thereby causing the device to become complicated in structure.
In the case where the detector means employed is of the electrode type, a means for cleaning the electrodes is needed to thereby make the device complicated in structure. In addition, the carryover of blood cannot be avoided in the course of cleaning the electrodes, thereby causing the accuracy of analyses to be reduced.